GENEVA — Sotheby’s says a rare blue diamond has sold for a record $48.5 million at a Swiss auction, including fees.

The 12.03-carat Blue Moon diamond, set in a ring, is said to be among the largest known fancy vivid blue diamonds and was the showpiece gem at Wednesday’s auction in Geneva. The price fell within the pre-auction estimate of $35 million to $55 million.

A packed auction room broke into applause after the hammer came down.

The Blue Moon — so-called in reference to its rarity, playing off the expression “once in a blue moon” — topped the previous record price of $46.2 million set five years ago by The Graff Pink.

On its Twitter account, Sotheby’s said the jewel was purchased by a Hong Kong collector and promptly renamed “The Blue Moon of Josephine” — a similar name to one given to a pink diamond ring that sold for $28.5 million at Christie’s in Geneva a day earlier: “Sweet Josephine.” That too was bought by a Hong Kong collector.

The polished blue gem was cut from a 29.6-carat diamond discovered last year in South Africa’s Cullinan mine, which also yielded the 530-carat Star of Africa blue diamond in the British crown jewels.